Here's how the US-led coalition decides when and where to hit ISIS targets in Iraq

A Kurdish fighter from the People's Protection Units (YPG) looks on after an coalition airstrike in Raqqa, June 16, 2017. Thomson Reuters

US-led coalition airstrikes against ISIS in Iraq and Syria hit record levels in August, dropping 5,075 bombs during close-air-support, escort, or interdiction operations.

That was the highest monthly total recorded during Operation Inherent Resolve, the three-year campaign against ISIS.

The amount of bombs dropped in each of the first eight months of 2017 exceeded the total of any other month during the campaign.

The 32,801 weapons deployed by coalition aircraft through August 2017 is more than the 30,743 dropped all last year, which was the previous annual high for Operation Inherent Resolve.

The sustained uptick in bombing during the first months of President Donald Trump's administration seems to fulfill his campaign promise to "bomb the s--- out of" ISIS. But the increase in bombings is also likely driven by intense operations in Mosul and Raqqa, ISIS' last major urban strongholds in Iraq and Syria, respectively.

Close-quarters fighting against determined ISIS militants in reinforced positions often necessitates close air support from Iraqi and coalition aircraft. (Not all aircraft active over Iraq and Syria are under US control, so the total number of weapons used is likely higher.)

Calls for airstrikes "would come from forces on the ground that an enemy's been identified, say, in this house," US Marine Corps Brig. Gen. Robert Sofge, director of the Combined Joint Operations Center in Baghdad, told Business Insider earlier this month. CJOC, as it's called, liaises with Iraqi security forces and government officials and is one of two strike cells in Iraq that manage such engagements, Sofge said.

Smoke rises after an airstrike during the battle against ISIS militants in the district of al-Mamoun in Mosul, March 1, 2017. REUTERS/Alaa Al-Marjani

"The enemy's been in a house, and that enemy's firing from this structure," Sofge said, describing a potential strike scenario. "So the first thing we do in a strike like that, we become aware of it, and we know where it is with great precision, 10-digit grids, down to the meter."

Coalition personnel and their local partners have a database of "category-one structures" that they will avoid targeting because they have infrastructural or historic value, including religious centers or hospitals. ISIS fighters are known to make use of those structures for that reason, Sofge said.

"If it's not that, it's still a [category two] structure that we would have to go through a rigorous process to say, 'Hey, this structure can be removed from its inherent protected status because of what's going there on now. There's fighters in there shooting at the Iraqi security forces.' So first we establish that we can go engage with this thing," Sofge told Business Insider.

"Then we apply a some fairly strict criteria of positive identification: How do we know who that is and what they're doing, and we have multiple intelligence requirements — it can't just be one thing; we have multiple indications that that is in fact what's going on from that place," he said, adding:

"And then we have a legal review that says that engaging this target comports with the laws of armed conflict and that engaging in these circumstances is permissible according to those laws, and once we've established all of those things we go to the government of Iraq and ask them for permission to strike that building, and they'll say yes or no, and they do say both, depending on the structure. They do a pretty thorough review themselves."

Iraqi special forces Lt. Col. Salam Hussein, center, and his team watch ISIS positions using a surveillance camera near the frontline in the Old City of Mosul, July 5, 2017. (AP Photo/Felipe Dana)

Sofge said coalition personnel will then, "within the bounds of proportionality," do engineering analysis to see what will be damaged in a strike and what effect it would have on nearby structures. That's followed by the weapon-selection process.

"We have an array of weapons available in support of the Iraqi security forces," he said. "We'll choose from among those and then use them in order to make sure that we do enough damage to kill the target and kill what it is that's attracted the Iraqi Security Forces' attention."

Sofge, who stressed coalition forces' efforts to avoid civilian casualties, said the actual process likely takes less time to complete than it does to describe, in part because of the experience they have doing it and because parts of it happen concurrently.

The US-led coalition's air campaign against ISIS has attracted intense scrutiny for the number of civilian casualties it is believed to have caused.

An Iraqi air force helicopter fires missiles against ISIS militants during a battle in Mosul, March 17, 2017. REUTERS/Youssef Boudlal

According to Airwars, a UK-based independent monitoring group, between Trump's inauguration and mid-July, more than 2,200 civilians appeared to have been killed in coalition airstrikes — almost as many as the 2,300 likely killed by coalition strikes under Obama.

That works out to 80 civilian casualties a month under Obama and 360 a month during the Trump administration.

Civilian deaths under Trump peaked in March, with nearly 700 confirmed or likely casualties. They have declined since June and July, when fighting in Mosul wrapped up.

Concerns about the air campaign were also piqued by reports the coalition had loosened its rules of engagement, allowing US and other coalition personnel on the ground to move closer to the front line and call in strikes and artillery fire directly, rather than going "through a whole bureaucracy and through Baghdad," one embedded US adviser told the Associated Press at the time.

A coalition spokesman told the AP the rules of engagement had been "adjusted" in December, "empowering" more coalition forces "to call in airstrikes without going through a strike cell."

The Pentagon contested that report, saying in March that overarching guidelines about such strikes had not changed, even as US personnel were being embedded at lower levels within Iraqi Security Forces units and appeared to be closer to direct combat.

A member of the Iraq Federal Police in the Old City of Mosul, July 8, 2017. Thomson Reuters

Asked if the process to carry out strikes had changed during the fighting in Mosul, Sofge said "not appreciably," adding that the process did see "refinements" regarding Iraqi permission for airstrikes.

"Some of the processes tend to be centralized, and in effort to decentralize them while still retaining the integrity of an Iraqi permission [it] was tweaked by the Iraqi government, not by the strike cells, as to who's the Iraqi giving you the thumbs-up that the government has given permission," Sofge told Business Insider.

"I know in some cases [it] was lowered a level in an effort to streamline the process so it was more effective to the fighters on the ground," he added, "but there was no change from a coalition perspective in the process — only who was the person saying 'yes' to the strike on the Iraqi side."

Such an adjustment may have given Iraqi commanders on the front line more say in when and where strikes took place.

Iraqi soldiers during fighting between the Iraqi army and Shi'ite Popular Mobilization Forces against ISIS militants in al-Ayadiya, northwest of Tal Afar, Iraq, August 28, 2017. Thomson Reuters

The Iraqi government declared the liberation of Mosul in early July, though cleaning up munitions left there by the fighting could take a decade or more.

ISIS fighters remain in some pockets of Iraq, mostly in the north-central part of the country and in the far western desert.

Iraqi forces, backed by the coalition, have launched assaults on those positions in recent days.

In Syria, the months-long fight in Raqqa has gained ground, according to US Army Col. Ryan Dillon, a coalition spokesman.

More than 75% of the city is now cleared of ISIS fighters, he said on Thursday, adding that Syrian Democratic Forces, a mainly Kurdish force partnering with the coalition, "have made clear progress and we are seeing ISIS begin to lose its grip on their self-declared capital in Raqqa."